Wednesday, 12 October 2016

Antennipatus montceauensis: A Velvet Worm from the Late Carboniferous of France.

Velvet
Worms, Onychophora, are curious caterpillar-like organisms found in
the tropics and temperate regions of the Southern Hemisphere. They
show external segmentation, but are not internally segmented, have a
soft cuticle rather that an exoskeleton, have non-segmented paired
appendages, and thick, non-segmented paired antennae. Velvet Worms
hunt Invertebrate prey, which they immobilize with a sticky slime
fired from special organs behind the antennae, the slime papillae.
There are two living families of Onychophora, the Peripatopsidae,
found in Australia, New Zealand, South Africa and Chile, and the
Peripatidae, found in West Africa, Southeast Asia, and the American
Tropics. All known extant species are terrestrial, the only known
Animal Phylum for which this is true, with their closest relatives
being the Arthropods and Tardigrades. Phylogenetic analyses have
shown the living Velvet Worms to be descended from the Lobopodians, a
curious group of entirely marine soft-bodied animals known from a
number of Cambrian locations, however how the Cambrian marine
Lobopodians gave rise to the Modern terrestrial Velvet Worms is
somewhat of a mystery, as there are almost no fossil specimens known
for the intervening period; Cretoperipatus burmiticus, from
Late Cretaceous Burmese Amber is a terrestrial form hard to
distinguish from Modern Velvet Worms, Helenodora inopinata,
from the Carboniferous Francis Creek Shale of Illinois is apparently
an Onychophoran and a descendent of the Cambrian Lobophorians, but is
not thought to be ancestral to, or closely related to, the living
Velvet Worms, while all other putative post-Silurian
Onychophoran fossils have now been excluded from the group.

Putative
Onychophorans from these deposits have been recorded for over thirty
years, however poor preservation of the material has prevented formal
description of the material until now. Garwood et al.
were able to supplement the light microscopy usually used to examine
fossils of this type, with more modern methods, such as computerized
tomography and digitally enhanced visualization.

The
new species is named Antennipatus montceauensis,
where 'Antennipatus'
refers to the Antennae of the specimens, which is very similar to
that of modern Velvet Worms, suggesting a close relationship (the
suffix -patus is
commonly used to describe modern genera within the group), and
'montceauensis' means
'coming from Montceau'. The specimens are essentially similar to
modern Velvet Worms, including having what appear to be slime
papillae. However it was not possible to place these Carboniferous
Worms in either of the modern families, as none of the features which
can be used to separate these group were (or were likely to be)
preserved. This means it is impossible to say whether they belong to
one of the two living families (which molecular clock data suggests
separated in the Devonian), an unknown group sharing a common
ancestor or a group which branched off before the divergence of the
modern Onychophoran families.

The
Carboniferous Onychophoran Antennipatus montceauensis
from the Stephanian Montceau-les-Mines Lagerstätte,
France. (A–C). First specimen, showing the head, including an
antenna and five anterior segments of the trunk. Shown in light
photograph (A), as rendered image from CT data employing low-angle
lighting (B), and as a rendered image using a multicolored lighting
rig (C). (D–E). Second specimen, showing the same region of the organism,
but with one set of lobopods as protrusions rather than depressions.
Shown as light photograph (D), lowangle lighting render (E), and
multicolored lighting render (F). (G). An enlargement of (D), showing
the antenna, a possible mouth, and slime papilla. (H). An SEM image
of the trunk showing large primary papillae and ridges demarking
plicae. (I.) A photomicrograph of the anterior of the fossil showing
the left slime papilla, possible mouth, and antenna. (J). A
photomicrograph of the trunk, showing the plicae and several well
preserved lobopods. a, antenna; lb1–lb5, lobopods 1–5; m?,
putative mouth; sp, slime papilla. Scales: A–G, 10 mm; H, 1 mm;
I–J, 2 mm. Garwood et al.
(2016).

The
Montceau-les-Mines Lagerstätte
is believed to have formed in and around a river delta flowing into a
freshwater lake. The site produces in situ woody fossils (i.e. the
trunks and roots of trees preserved in the position where they grew,
interspersed with fluvial (river) and lucastrine (lake) sedments.
There is no influence for any marine influence on the site. Therefore Antennipatus montceauensis could potentially have inhabbited a terrestrial environment similar to that favoured by modern Velvet Worms, or coud possibly have inhabited fresh water, a habitat no other Onychophoran, living or fossil, is known to have inhabited, but which is a plausible step between the fully marine habbit of ancient members of the group and the entirely terrestrial habitat favoured by moden Velvet Worms.

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About Me

Studied Palaeobiology & Evolution at the University of Portsmouth, Geosciences via the Open University & Ecology and Conservation at Christchurch University, Canterbury.
Have worked in wildlife based tourism, mineral exploration, development, conservation, education & environmental chemistry. Occasionally write articles for papers and magazines.

This Blog would be impossible without the work of countless scientists (and others) throughout the world. Where possible I do my best to credit them, but there will always be many more who remain unmentioned; this does not imply I am ungrateful for their contributions. Any errors or inaccuracies are, of course, my own.